Multiple battery charging stations for rechargeable batteries are known in the art. It is common for batteries to be placed in the charging station with varying charge levels still in the batteries. The time required for each battery to be charged again to a useful level is thus also variable. However, many early conventional charging stations charge all of the batteries at the standard or nominal charge rate at the same time. Thus, batteries closer to their useful charge level can be overcharged, affecting the battery's life. However, to avoid overcharging these batteries, the batteries farther from their useful charge level are undercharged, limiting the time they can power a device.
One conventional approach to this problem is to charge the batteries with the lowest charge level first or at a higher charge rate than the other batteries, until all of the batteries are at the same charge level. Then, all of the batteries are charged at the same charge rate. However, with this approach, even if one of the batteries is close to its useful charge level, a user must still wait until the charge levels of the other batteries “catch up”, before a battery is available for use.
In addition, multiple battery charging stations can result in power distribution and thermal problems. Some conventional charging stations provide maximum continuous charge to all batteries, whether or not it is required at a particular time. This places a large demand on the charging station's power supply. In stations with a large number of batteries, the power required can exceed the AC line current capacity.
Accordingly, there exists a need for an improved method for multiple battery charge control. The method should prioritize the charging of the batteries depending on the status of the battery. It should decrease the time required for at least some of the batteries to be at a desired charge level and available for use as quickly as possible. It should also assist in preserving battery life and manage the charge rates so that the power required by the charging station does not exceed the AC line current capacity. The present invention addresses such a need.